Vulnerability-Lookup

GHSA-HWR6-493R-VM6H

Vulnerability from github – Published: 2026-09-30 23:44 – Updated: 2026-09-30 23:44

Summary

fastify vulnerable to request validation bypass via skipped boolean false schemas

Details

Impact

Fastify decided whether to validate a request part by checking its schema for JavaScript truthiness. JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance, but because false is falsy, a route that set body, querystring, params, or headers to false had that part left uncompiled: no validator was attached and the request reached the handler. An application that used false as a deny-all schema to make a route unreachable was therefore fully bypassed, and an unauthenticated remote client could reach the handler with any input. The same applied to the documented query alias for querystring. This is a complete bypass rather than a weak-schema issue, since false is the strongest JSON Schema assertion and must always fail.

Patches

Request-part schemas are now selected by an explicit presence check rather than truthiness, so a boolean false (or true) schema is compiled and enforced, including through the query alias. Patched in fastify 5.12.2. The fix is also included in the 6.0.0 release.

Workarounds

If upgrading is not immediately possible, express a deny-all request schema with an always-failing object schema instead of the boolean false (for example { "not": {} }), or reject the request in an onRequest hook.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

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JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "fastify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.12.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-84469"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-30T23:44:58Z",
    "nvd_published_at": "2026-09-04T10:17:13Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nFastify decided whether to validate a request part by checking its schema for JavaScript truthiness. JSON Schema Draft 7 defines the boolean `false` as a valid schema that rejects every instance, but because `false` is falsy, a route that set `body`, `querystring`, `params`, or `headers` to `false` had that part left uncompiled: no validator was attached and the request reached the handler. An application that used `false` as a deny-all schema to make a route unreachable was therefore fully bypassed, and an unauthenticated remote client could reach the handler with any input. The same applied to the documented `query` alias for `querystring`. This is a complete bypass rather than a weak-schema issue, since `false` is the strongest JSON Schema assertion and must always fail.\n\n### Patches\n\nRequest-part schemas are now selected by an explicit presence check rather than truthiness, so a boolean `false` (or `true`) schema is compiled and enforced, including through the `query` alias. Patched in fastify `5.12.2`. The fix is also included in the `6.0.0` release.\n\n### Workarounds\n\nIf upgrading is not immediately possible, express a deny-all request schema with an always-failing object schema instead of the boolean `false` (for example `{ \"not\": {} }`), or reject the request in an `onRequest` hook.",
  "id": "GHSA-hwr6-493r-vm6h",
  "modified": "2026-09-30T23:44:58Z",
  "published": "2026-09-30T23:44:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/security/advisories/GHSA-hwr6-493r-vm6h"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-84469"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/commit/7de6e81697778f9f41bd327a3b1c5c9a0d9637b4"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fastify/fastify"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/releases/tag/v5.12.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "fastify vulnerable to request validation bypass via skipped boolean false schemas"
}

CVE-2026-84469 (GCVE-0-2026-84469)

Vulnerability from cvelistv5 – Published: 2026-09-04 09:59 – Updated: 2026-09-04 19:34

Title

fastify vulnerable to request validation bypass via skipped boolean false schemas

Summary

fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance. When an application assigns false to a route's body, querystring, params, or headers schema to deny all input, fastify treats it as a missing schema, compiles no validator, and runs the route handler on any request. An unauthenticated remote client can therefore reach a handler that a valid deny-all schema was intended to make unreachable, a complete validation bypass that can lead to unauthorized state changes or execution of disabled operations. Users should upgrade to fastify 5.12.2 or later.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-04 19:34 UTC

CWE

CWE-20 - Improper Input Validation

Assigner

openjs redhat root Scorecard

References

2 references

URL	Tags
https://github.com/fastify/fastify/security/advis…
https://cna.openjsf.org/security-advisories.html

Impacted products

1 product

Vendor	Product	Version
fastify	fastify	Affected: 0 , < 5.12.2 (semver) Unaffected: 5.12.2 (semver)

Credits

schecthellraiser606 mcollina UlisesGascon climba03003

Show details on NVD website

JSON

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Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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